Thermodynamics and Molecular Mechanics Studies on α- and β-Cyclodextrins Complexation and Diethyl 2,6-naphthalenedicarboxylate Guest in Aqueous Medium (original) (raw)
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Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2007
Steady-state, time-resolved fluorescence and Molecular Mechanics techniques have been used to study the complexation of 1-methyl naphthalenecarboxylate with three naturally occurring cyclodextrins (CDs). Emission spectra of 1MN show two overlapping electronic bands. The stoichiometry, the formation constants of the complexes and the thermodynamics parameters upon inclusion were obtained from the change of intensity ratios R of the maxima of both bands and AEsae with [CD] and temperature. As with the 2-methyl naphthalenecarboxylate (2MN) guest, 1:1 stoichiometries were obtained for all complexes. The formation constants, however, were relatively low compared to those obtained for 2MN. Geometry of the complexes from Molecular Mechanics in the presence of water agrees with the experimental stoichiometry of the complexes and the signs of enthalpy and entropy changes. Quenching, R at [CD] fi ¥ and fluorescence depolarization measurements also support the proposed structures. As with 2MN the inclusion is mostly dominated by van der Waals interactions.
The Journal of Physical Chemistry, 1995
A 1 : 1 complex of 6-O-a-~-glucosyl-~-cyclodextrin (GI-B-CD) with 4-(dimethy1amino)benzonitrile (DMABN) associates with itself in aqueous solutions at high concentrations into a 2:2 complex (homodimer). The 1:l complex of GI-B-CD with DMABN also makes a heterodimer (1:1:2 complex) by the association with a 1:l inclusion complex of another guest molecule such as 1-pentanol, benzene, anisole, and benzonitrile. The association of the complex is accompanied by a drastic change in the fluorescence spectrum of DMABN. The measurement of the fluorescence intensity as a function of the concentration of GI-B-CD gave the equilibrium constants for the association. The equilibrium constants were greatly dependent on the temperature, and the values for both AH and AS were largely negative. The fluorescence spectra of DMABN in the cavity of the dimers changed with exchanging the second guest compound, which implies that the second guest molecule plays the role of a polar solvent in the nonpolar environment in the cavity. The formation of homo-and heterodimers of the 1:l inclusion complex also takes place in the solutions containing other cyclodextrins and DMABN.
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2007
Molecular mechanics (MM) and Molecular dynamics (MD) calculations were applied to study the complexation of 2-Methyl naphthalenecarboxylate (2MN) and 2-hydroxypropyl-a- ,-band nd c-cyclodextrins (HPCDs) in the presence of water. Results showed that 1:1 complexes of 2MN with modified cyclodextrins are stable and that the non-bonded van der Waals interactions are mainly responsible for the complexation. Theoretical results are in good agreement with fluoresence results and they permit us to explain the signs and quantitative differences of DH 0 and DS 0 on the basis of the different cavity sizes and the movement of the guest inside the HPCD cavity. Results also reveal a more favorable complexation when 2MN approaches on its polar side.
Journal of Physical Chemistry B, 1998
Steady-state fluorescence and molecular mechanics calculation were used to study the inclusion complexes of 2-methylnaphthoate (MN) with γ-cyclodextrin (γ-CD). The stoichiometry (1:1) and binding constants (213 (96 M-1 at 25°C) were extracted from an analysis of the ratio of the intensity of two emission bands that were sensitive to the polarity of the medium. Extrapolation of this ratio to a high concentration of γ-CD permits the estimation of the polarity of the inner cavity, which seems to be only slightly hydrophobic, with a dielectric constant near 74. The ∆H and ∆S for formation of the complex were obtained and compared with previous results for similar complexes of MN with two smaller CDs. Molecular mechanics calculations were applied to study the complex in vacuo and in the presence of water as a solvent. Complexation is mainly due to nonbonded van der Waals interactions of MN with γ-CD. Calculations show that MN penetrates completely into the cavity of γ-CD. Experimental Section Materials. MN was prepared from 2-naphthoyl chloride and methanol in chloroform in the presence of triethylamine at room temperature. Purification was achieved by several recrystallizations from chloroform/methanol. The structure was verified by nuclear magnetic resonance. γ-CD and 2-methyl cetone, purchased from Aldrich, were used without further purification. Water (passed through a Milli-Q water system) was checked for the absence of fluorescent impurities before use. Owing to the low solubility of MN in water, aqueous solutions of MN and γ-CD were prepared using a saturated solution (approximately 3 × 10-5 M) of MN as the solvent. This saturated aqueous solution was prepared in an ultrasonic bath at 60°C. After approximately 8 h, it was cooled and then filtered twice through 0.5-µm diameter pore size cellulose filters (Millipore). Aqueous MN-γ-CD solutions were prepared by weight in their own quartz cuvettes and were then sealed with Teflon stoppers. All solutions were stirred in their own cuvettes 2037
Journal of Inclusion …, 1998
Using a simple molecular mechanics approach interaction energy profiles of simple probes (C, CH 4 , C 6 H 6 , H 2 O, NH + 4 , and HCOO − ) passing through the center of the β-CD ring cavity along the main molecular symmetry axis were first evaluated. Molecular Electrostatic Potential (MEP) values along the same path were also evaluated. The effect of the flexibility of the host β-CD molecule together with solute-solvent (H 2 O) interactions have been represented by averaging structures of MD calculations for β-CD alone and β-CD surrounded by 133 H 2 O molecules. The effect of various substitutions of β-CD has also been evaluated. Small symmetric hydrophobic probes (such as C, CH 4 , C 6 H 6 ) are predicted to form stable inclusion complexes with non-substituted and substituted β-CDs, the probe position typically being near the cavity center. The stability of the inclusion complexes will increase with increasing size and aliphatic character of the probe. Small polar and charged probes (such as H 2 O, NH + 4 , HCOO − ) are predicted to prefer the interaction with the solvent (water) in the bulk phase rather than the formation of inclusion complexes with non-substituted and substituted β-CDs. Guest-host interactions in the stable inclusion complexes with hydrophobic probes are almost entirely dominated by dispersion interactions. The MEP reaches magnitudes close to zero in the center of the non-substituted β-CD ring cavity and in most of the studied substituted β-CDs and shows maximum positive or negative values outside of the cavity, near the ring faces. Substitution of β-CD by neutral substituents leads to enhanced binding of hydrophobic probes and significant changes in the MEP profile along the β-CD symmetry axis.
Journal of Physical Chemistry B, 1999
Steady-state fluorescence and molecular mechanics calculations were used to study the inclusion complexes of 9-methyl anthracenoate (MA) and 1-methyl pyrenoate (ΜP) with -cyclodextrin ( CD). Binding constants of 1:1 complexes at different temperatures were obtained from the analysis of the fluorescence enhancement of the CD solutions with respect to the MA or MP free chromophores. The thermodynamic parameters ∆H and ∆S were also obtained. Molecular mechanics calculations were applied to study both inclusion processes in vacuo and in the presence of water as a solvent. Complexation is mainly due to nonbonded van der Waals host-CD interactions. Both MA and MP penetrate only partially into the CD cavity.
Formation of β-cyclodextrin complexes in an anhydrous environment
Journal of Molecular Modeling, 2016
The formation of inclusion complexes of βcyclodextrin was studied at the melting temperature of guest compounds by differential scanning calorimetry. The complexes of long-chain n-alkanes, polyaromatics, and organic acids were investigated by calorimetry and IR spectroscopy. The complexation ratio of β-cyclodextrin was compared with results obtained in an aqueous environment. The stability and structure of inclusion complexes with various stoichiometries were estimated by quantum chemistry and molecular dynamics calculations. Comparison of experimental and theoretical results confirmed the possible formation of multiple inclusion complexes with guest molecules capable of forming hydrogen bonds. This finding gives new insight into the mechanism of formation of host-guest complexes and shows that hydrophobic interactions play a secondary role in this case.
Density‐functional‐theory study of α‐cyclodextrin inclusion complexes
We apply the density functional theory on the description of the a-cyclodextrin (a-CD) and the analysis of the molecular electrostatic potential (MEP) for complexes of this system with Na þ , F À , CO 2À 3 , and N,N-dimethyl formamide, as substrates. Four exchange-correlation functionals were considered: one of the local density approximation, two of the generalized gradient approximation (BLYP and PBE), and one of the hybrid family. These exchange-correlation functionals were coupled with the DZVP/A1, DZVP, and TZVP basis set functions. All complexes were fully optimized by all methods. The experimental molecular structure of the a-CD compares better with that described by the PBE exchange-correlation functional. The MEP analysis shows that the electrostatic is quite relevant on the intermolecular interaction for the a-CD complexes in gas phase. Some of our results are in disagreement with those published previously with the PM3 semiempirical method and the B3LYP//PM3 method.
Conformational and circular dichroism studies on cyclodextrin inclusion complexes
Pure and Applied Chemistry, 1997
A &mework aimed at elucidating the structure of inclusion complexes between cyclodextrins (CDx) and several chromophores of photochemical interest is presented. The scheme is composed by a set of Molecular Mechanics calculations, Monte Car10 simulations including solvent effects and reproduction of the Induced Circular Dichroism (ICD) using quantum mechanically calculated properties combined to the Kirkwood-Tinoco expressions for the induced rotational strength. Examples of molecular recognition between a,P and y-CDx and a variety of chromophores of fundamental as well as of applicative interest , such as phenols, dimethoxybenzenes and buclaninstedlerene are examined. The method proposed proves to be a suitable instrument to elucidate different geomdcal configurations and to be able to gain insight into the relationship between structural and dynamic properties of the complexes studied. &&j&&g Supramolecular self-assembly has received recently a great deal of interest in several fields of Chemistry and Biology7 as it provides the physical basis for molecular recognition , formation of enzyme-complexes with substrates and is also related to protein folding. A remarkable model for this phenomenon is represented by the inclusion of a variety of organic compounds of molecules of suitable size in cyclodextrins (CDx), cyclic oligosaccharides consisting of sii (a-CDx) , seven (p-CDx) or eight ('y-CDx) D(+) glucopyranose units linked by u-(1,4) bonds and containing a central, hydrophobic cavity with a diameter of 5-8 A (1). The stability of the inclusion is determined by the fit of the molecular shape of the guest to the surface of the cavity, with intervention of van der W a a l s forces, hydrogen bonding, decrease of strain energy and release of high energy water molecules &om the cavity.The high solubility in water of the inclusion complexes of hydrophobic molecules in CDx has been exploited for a number of applications in pharmaceutical chemistry , food technology and plant protection industries. Moreover, due to their capability in binding substrates quickly, selectively and reversibly and to behave as catalysts in many chemical reactions, CDx can be considered good model enzymes. It is , therefore, of fundamental importance to understand the physics of complexation, i.e. the driving forces which govern the
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 1993
The inclusion complexes of 2-naphthyloxyacetic acid (NOA) and 1-naphthylacetic acid (NAA) with β-cyclodextrin have been investigated in aqueous solution. It has been demonstrated that the naphthalene derivatives form 1:1 complexes when included in the cyclodextrin. A possible structure is proposed, having an axial inclusion of the naphthalene derivatives. In the case of the β-CD: NOA complex, the naphthyl moiety is included in the cyclodextrin and the acetic acid group protrudes from the cavity, while NAA is only partially included because of the steric effect of the group in position 1. Association constants of 560±100 M−1 and 100±50 M−1 have been calculated for the β-CD: NOA and β-CD: NAA complexes, making use of the increment in the fluorescene emission produced in the inclusion process.